For one thing, if (god forbid) I write anything worth seeing I want everyone to be able to see it, not just my Facebook friends. (With a few exceptions. And for those exceptions, Live Journal has much better access controls.)

A bunch of related points about walled gardens are explained by Cory Doctorow:

"Facebook's 'platform' strategy has sparked much online debate and controversy. No one wants to see a return to the miserable days of walled gardens, when you couldn't send a message to an AOL subscriber unless you, too, were a subscriber … the kind of place where the clueless management were willing and able to — for example — alienate every Vietnamese speaker on Earth by banning the use of the word 'Phuc' (a Vietnamese name) because naughty people might use it to evade the chatroom censors' blocks on the f-bomb.

Facebook is no paragon of virtue. It bears the hallmarks of the kind of pump-and-dump service that sees us as sticky, monetizable eyeballs in need of pimping. The clue is in the steady stream of emails you get from Facebook: 'So-and-so has sent you a message.' Yeah, what is it? Facebook isn't telling — you have to visit Facebook to find out, generate a banner impression, and read and write your messages using the halt-and-lame Facebook interface … Emails from Facebook aren't helpful messages, they're eyeball bait, intended to send you off to the Facebook site, only to discover that Fred wrote 'Hi again!' on your 'wall.' Like other 'social' apps (cough eVite cough), Facebook has all the social graces of a nose-picking, hyperactive six-year-old, standing at the threshold of your attention and chanting, 'I know something, I know something, I know something, won't tell you what it is!'

If there was any doubt about Facebook's lack of qualification to displace the Internet with a benevolent dictatorship/walled garden, it was removed when Facebook unveiled its new advertising campaign. Now, Facebook will allow its advertisers use the profile pictures of Facebook users to advertise their products, without permission or compensation. Even if you're the kind of person who likes the sound of a benevolent dictatorship this clearly isn't one."

I like this set of explanations. But I feel helpless to find the right way to comment! Particularly interesting : 'too addictive' - what is the right way to moderate addiction, when one has created something that others really wnt to use, but it's "not good for them" in a way that will eventually drive them away?